There exist what we call images (simulacra) of things; which, like films drawn from the outermost surface of things, flit about hither and thither through the air, it is these same that, encountering us in wakeful hours, terrify our minds, as also in sleep, when we often seem to behold wonderful shapes and images of the dead... lest by chance we should think that spirits escape from Acheron or ghosts flit about amongst the living... . I say, therefore, that semblances and thin shapes of things are thrown off from the outer surface, which are to be called as it were their films or bark, because the images bears a look and shape like the body of that from which it is shed to go on its way.